By Jeff Floyd
Certified horticulturist and arborist
The next time you plant a tree, consider something other than oak. Between twenty and thirty percent of trees here in Odessa and Midland are oak trees. The majority of those are Live oaks. This is more than twice the upper limit recommended by the Texas A&M Forest Service. You might be asking yourself why would anyone propose a limit on the proportion of any given tree in a community? One answer: disease.
In the case of oaks, that disease is oak wilt. Oak wilt is a fungal disease that damages the vascular system of oak trees, limiting their ability to take up water. It is spread by root grafts, insects, or poor pruning techniques. Only oaks get the disease, but red oaks are the least likely to survive it. Oak wilt tends to move slower in Live oaks, but it can kill any type of oak tree if left untreated.
Oak roots develop connections with one another. When roots of neighboring oaks contact one another, their vascular systems fuse and move water and minerals back and forth. If one of them has a fungus, they’ll share that too. More than ninety-five percent of oak wilt in Texas is probably spread through these underground grafts.
Several types of sap-feeding insects are also known to spread oak wilt. One family of beetles known as Nitidulidae, are notorious for picking up the oak wilt fungus while feeding on infected trees and moving it to healthy ones. The scent of sap attracts them within minutes of a fresh pruning cut or injury to a branch.
The Forest Service advises people to avoid pruning oaks between the 1st of February and the end of June; this is when insects are most active. They also recommend the use of a pruning sealant immediately after making each cut. As an additional precaution, pruning tools should be sterilized between trees.
Trees can be somewhat protected by a fungicide. However, this treatment, even when performed properly by a qualified arborist, cannot be guaranteed. One method that could be used to avoid losing large swaths of trees is to diversify the species planted in an area. When all the trees in a neighborhood are oaks, the likelihood of oak wilt killing them is much higher. This has happened along some streets in Midland and Odessa.
By planting multiple different species in a city, the risk of any single pathogen wiping out a large percentage of shade is reduced. The oak wilt fungus only kills oaks. For a list of other trees that perform well in West Texas, visit tinyurl.com/yck299j2.
